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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Dynamic Memory</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.78.1" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="support.html" title="Chapter 4.  Support" /><link rel="prev" href="support.html" title="Chapter 4.  Support" /><link rel="next" href="termination.html" title="Termination" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Dynamic Memory</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="support.html">Prev</a> </td><th width="60%" align="center">Chapter 4. 
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</th><td width="20%" align="right"> <a accesskey="n" href="termination.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="std.support.memory"></a>Dynamic Memory</h2></div></div></div><p>
    There are six flavors each of <code class="function">new</code> and
    <code class="function">delete</code>, so make certain that you're using the right
    ones. Here are quickie descriptions of <code class="function">new</code>:
  </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
	single object form, throwing a
	<code class="classname">bad_alloc</code> on errors; this is what most
	people are used to using
      </p></li><li class="listitem"><p>
	Single object "nothrow" form, returning NULL on errors
      </p></li><li class="listitem"><p>
	Array <code class="function">new</code>, throwing
	<code class="classname">bad_alloc</code> on errors
      </p></li><li class="listitem"><p>
	Array nothrow <code class="function">new</code>, returning
	<code class="constant">NULL</code> on errors
      </p></li><li class="listitem"><p>
	Placement <code class="function">new</code>, which does nothing (like
	it's supposed to)
      </p></li><li class="listitem"><p>
	Placement array <code class="function">new</code>, which also does
	nothing
      </p></li></ul></div><p>
     They are distinguished by the parameters that you pass to them, like
     any other overloaded function.  The six flavors of <code class="function">delete</code>
     are distinguished the same way, but none of them are allowed to throw
     an exception under any circumstances anyhow.  (They match up for
     completeness' sake.)
   </p><p>
     Remember that it is perfectly okay to call <code class="function">delete</code> on a
     NULL pointer!  Nothing happens, by definition.  That is not the
     same thing as deleting a pointer twice.
   </p><p>
     By default, if one of the <span class="quote">“<span class="quote">throwing <code class="function">new</code>s</span>”</span> can't
     allocate the memory requested, it tosses an instance of a
     <code class="classname">bad_alloc</code> exception (or, technically, some class derived
     from it).  You can change this by writing your own function (called a
     new-handler) and then registering it with <code class="function">set_new_handler()</code>:
   </p><pre class="programlisting">
   typedef void (*PFV)(void);

   static char*  safety;
   static PFV    old_handler;

   void my_new_handler ()
   {
       delete[] safety;
       popup_window ("Dude, you are running low on heap memory.  You"
		     " should, like, close some windows, or something."
		     " The next time you run out, we're gonna burn!");
       set_new_handler (old_handler);
       return;
   }

   int main ()
   {
       safety = new char[500000];
       old_handler = set_new_handler (&amp;my_new_handler);
       ...
   }
   </pre><p>
     <code class="classname">bad_alloc</code> is derived from the base <code class="classname">exception</code>
     class defined in Sect1 19.
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